PORTABILITY
One of the most sought after features UNIX possesses is portability. Portability is the ability to rewrite the operating system for a different vendor's hardware without a major rewrite effort. UNIX is highly portable and has been ported by many hardware vendors to their computer hardware. In fact, every computer vendor has a UNIX or a UNIX-like system ported to their hardware - a milestone that no other operating system can claim.
There are two main reasons UNIX is a prime system for porting from hardware to hardware. The first is that the kernel provides an interface between the hardware and most of the nonkernel UNIX software. When UNIX is ported to another hardware platform, only the kernel requires major modifications. Since most of the UNIX software interfaces with the kernel and not the hardware, the software is hardware independent and does not require much, if any, modification when it is ported to a new hardware platform.
The second reason UNIX is easy to port is that the majority of the UNIX operating system is written in the C programming language. Most operating systems are written in the hardware vendor's proprietary assembly language. This makes it very difficult, if not impossible, to port their operating systems to a different vendor's computer.
Benefits
Portability allows the customer to choose the vendor and not be locked into that vendor's hardware and software environment. It also provides the user with a broad base of application software that can be used on hardware from different application vendors.
The porting of an operating system creates a standard software environment across a broad range of computers, ranging in size from micros to supercomputers. This cuts training time dramatically and increases overall productivity. It also reduces support costs and redevelopment costs.
PORTABLE APPLICATION SOFTWARE
The UNIX System provides a standard application development environment that allows for easy porting of application software. The C programming language is a big asset to the porting of software between different UNIX machines.
The ability to port software to many systems easily provides application software vendors with a much larger market without the headaches of multiple proprietary environments. Customer training requirements are reduced and the training of internal personnel is minimized. The number of support people needed is not increased because of different knowledge base requirements, but because more software is being sold. Development can spend more time on enhancements instead of ports to unknown, proprietary architectures. Once a customer has bought a product on one UNIX machine, the customer can purchase a different vendor's UNIX machine and be able to use the same applications without having to retrain personnel. As you can understand, portability is a very important issue for many computer users.
JOB CONTROL
Job control on UNIX is the ability to control which job is executed in foreground, background, or is suspended.
* Foreground execution is considered normal interactive command execution. The command is entered from the keyboard. The shell waits until the command completes execution, then the shell prompts for another command to execute.
* Background execution is considered batch processing. A command is entered and detached from the terminal. The shell can continue interactive command processing.
* Suspended jobs (processes) are commands that have been placed in a suspended state. They are not being executed in background or foreground.
Job control allows you to suspend a foreground or background job. A suspended job can be moved to background or foreground. Background jobs can be brought to the foreground and foreground jobs can be placed in the background.
Using job control can increase the productivity of a user by allowing multiple tasks to be juggled back and forth between background, foreground, or a suspended state. For example, a user can edit a source file while executing the compiled program, thus watching the functionality of the program and making changes while suspending the program.
